Driven by a desire to find new structural polysaccharides using enzymatic syntheses or genetic engineering of microorganisms or plant hosts, researchers have discovered polysaccharides that are biodegradable and can be made economically from renewably sourced feedstocks. One such polysaccharide is poly alpha-1,3-glucan, a glucan polymer characterized by having alpha-1,3-glycosidic linkages. This polymer has been isolated by contacting an aqueous solution of sucrose with a glucosyltransferase (GTF) enzyme isolated from Streptococcus salivarius (Simpson et al., Microbiology 141:1451-1460, 1995).
U.S. Pat. No. 7,000,000 disclosed the preparation of a polysaccharide fiber using an S. salivarius gtfJ enzyme. At least 50% of the hexose units within the polymer of this fiber were linked via alpha-1,3-glycosidic linkages. S. salivarius gtfJ enzyme utilizes sucrose as a substrate in a polymerization reaction producing poly alpha-1,3-glucan and fructose as end-products (Simpson et al., 1995). The disclosed polymer formed a liquid crystalline solution when it was dissolved above a critical concentration in a solvent or in a mixture comprising a solvent. Continuous, strong, cotton-like fibers were obtained from this solution that could be spun and used in textile applications.
While some advances have been made in producing linear glucan polymers having a high percentage of alpha-1,3 glycosidic linkages suitable for use in spinning fibers, it is believed that less attention has been drawn to producing branched alpha-glucan polymers. To that end, disclosed herein are modified glucosyltransferases that can synthesize branched alpha-glucan.